Mixtures of different plant growth-promoting rhizobacteria (PGPR) were used to control soil-borne pathogens of tomato plants. First, their effect was studied in mini-chamber tests against Rhizoctonia damping-off. The best strains and their mixtures were selected for the greenhouse and field experiments conducted in years 2006-2007. The seeds and then the roots of tomato transplants were inoculated with the suspensions of single bacterial strains or with their combinations. In the greenhouse experiments treated plants were grown in the potting medium infested with pathogenic Fusarium oxysporum f. sp. lycopersici, and the effect of bacteria on the population of Fusarium spp. in the rhizosphere was studied. In field experiments the plants were planted into natural infested soil. In both kind of the experiments (greenhouse and field) the impact of the inoculation on plant yield and diseases incidence was evaluated. Although, the results of the preliminary and mini-chamber tests were promising, and the bacteria B125, PT42, SZ141 and their mixtures significantly reduced damping-off of tomato seedlings, in greenhouse and field experiments, in most cases the bacterial treatments failed to improve yield and to protect the plants. Among tested bacterial inoculations only the mixture of the bacteria B125 and PT42 tended to affect positively the growth of the plants and to reduce their infection by soil-borne pathogens. However, bacterial inoculations significantly decreased the density of Fusarium spp. in the rhizosphere of tomato plants.
